Abstract

Dolphins echolocate with short broadband acoustic signals which have good time resolutionproperties. Received echoes are often complex, with many resolvable highlights or components caused by reflection of the incident signal from external and internal boundaries of a target and from different propagational modes within a target. A series of experiments was performed to investigate how dolphins perceive complex echoes.Echoes were produced by a microprocessor‐controlled electronic target simulator which captured each emitted click and retransmitted the signal back to the animal after an appropriate delay time. The use of a “phantom” target allowed for precise control of the number of highlights, the time separation between highlights and the relative amplitudes of highlights in the simulated echoes. An echolocating dolphin was trained to perform a target detection task in the presence of masking noise using these phantom echoes. The properties of simulated echoes were systematically varied, and corresponding shifts in the dolphin's detection threshold were observed, allowing the inference of how the dolphin perceived the echoes. The dolphin performed like an energy detector with an integration time of approximately 290 μs.